Electron discharge device



April 1941- J. L. H. JONKER 2,239,388

ELECTRON DISCHARGE DEVICE Filed Dec. 17, 1938 INVENTOR. JOHAN L. H. JONKER A TTORNE Y.

Patented Apr. 22, 1941 UNITED STATES PATENT OFFICE 2,239,388 steam-on mscnmo'ri Device Joli'an' Lode'wijk Hendrik Jonker, Eindhoven, Netherlands, assignor, by mesne assignments,

to Radio Corporation of America, New York, N. Y., a corporation of Delaware Applicationllecember 17, 1938, Serial No. 246,290 In the Netherlands January 8', 1938 4 Claims.

This invention relates to an improved electron discharge device of the so-called space charge grid type and associated circuit arrangement.

Generally, a'so-called variable mu charac-' teristic is obtained by shaping one or' more grids in a tube in an irregular form or with variable grid wire spacing. A tube of this kind, however, cannot be used in circuit arrangements in which a constant mutual conductance is desired.

Again space charge grid type tubes which usually have a cathode, a positively biased space charge. grid, a control grid and anode in the other named, are capable of large output but are inefficient when'used as power output tubes because when the control grid goes negative substantially all of the space charge current goes to the positively biased space charge grid and is wasted.

Hence it is the principal object of my invention to provide an electron discharge device of the so-called space charge grid type which may have a constant pitch control grid and which can be used not only as a variable mu type tube but which is eflicient when used as apower output tube.

According to the invention the circuit arrangement and tube provide a variable mutual conductance characteristic. For this purpose, the tube contains, between the cathode and the anode, at least three electrodes including a screening electrode, an" electrode next to the cathode which is connected to the screen grid and both connected through a regulable resistance, to a point, of positive voltage, the mutual conductance being controlled also by means of the said resistance. I

Due to this circuit arrangement the voltage of the electrode next to the cathode and that of the screening electrode screening grid) itself will be dependent on the voltage drop across the said resistance, for example, on: the screening grid current. If the resistance is high the volt-' age at the said electrodes will be low so that space charge phenomena may occur in the neighborhood of the electrode next to the cathode, while at the same time the mutual conductance decreases due to the low screening grid voltage. If the resistance is lower, the voltage of the said electrodes increases so that the mutual conductance increases. The electrode next to the cathode serves substantially for sucking away the space charges that may arise between the cathode and the screening grid, particularly it their spacing is not constant. For this purpose, this electrode may advantageously be shaped in tirely new means of obtaining a tube with regulable mutual conductance, the advantage being inter alia obtained that the same tube can also be used in circuits in which a constant mutual conductance is desired.

The novel features which I believe to be'characteristicof my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by refer ence to the following description taken in connection with the accompanying drawing in which Figure 1' shows a diagrammatic top view with the envelope in section of a tube made according to my invention and its associated circuit, and Figures 2 and 3 show respectively characteristics of a conventional space charge grid tube and atube made according to my invention.

In Figure 1 of the drawing, the cathode I has between it and anode 5, electrodes 2, 3 and 4. As shown in the figure, the electrode 2 may be constituted by two rods. The distance of the rods relatively to the cathode should preferably exceed the smallest distance of thecathode relatively to" the control grid 3 in order that these rods do not attract too large a current. These electrodes, which are coextensive, are mounted Within envelope Ill.

The firstxand third auxiliary electrodes are inte-rconnected and are connected through a variable resistance 6 shunted by a condenser 6' to the positive terminal of a high voltage battery. The control grid 3 is connected to ground throughthe input circuit I, whereas the cathode is grounded through the resistance 8 which governs the negative bias of the control grid. Resist'ance 8 is by-passed by condenser 8'.

The anode is connected to the output circuit 9. In the case represented, for normal use the first auxiliary electrode may be connected to a fixed voltage, which may be positive. It is also possible to interconnect the first and the third auxiliary electrodes in the tube itself.

In Figure 2 is shown the grid voltage-anode current characteristic and space charge grid current characteristic for the conventional space charge grid tube in which the space charge grid adjacent the cathode is maintained at a positive potential with respect to the cathode. It will be seen as the control grid voltage E0 is made more negative, that the plate current In decreases to the cut-01f point where it has a zero value. The dotted line which represents the space charge grid current It increases and attains a maximum at the cut-off point of the plate current. L'I'he reason for this is thatas the voltage on the control grid is made more negative to cut oil the plate current, the space charge becomes denser and moves closernto the space charge grid. Thus, although the voltage on the space charge grid remains constant the the space charge come under the influence of the field from the space charge grid. As a re.-

sult in operation when the space chargeg'rid tube is used as a power output tube more and more current is wasted when the grid becomes increasingly negative. v The same characteristics for a tube made according to my invention are shown inFigure 3. Herealthough substantially the sameefiect occurs so far as the space charge is concerned when the control grid becomes negative, that is the space charge becomes more dense and is moved closer toward the cathode due to, the small area of the space charge'grid rods 2 and the fact that no shielding effect is produced between the cathode and the anode by the space charge grid, the field from the anode and screen grid is more efiective in causing electrons. to flow toward the anode and hence a more negative grid voltage is necessary to finallycut-ofi the plate output current. Furthermore, as a result of the positioning of the space charge rods and their reduced area although the, space charge does become more dense and moves closer to the cathode, the number of electrons in the space charge which come under the influence of the field of the space charge grid rods is not as great as with the conventional grids. This is shown by the relatively small increase in the space charge current to the space charge rods at the cut-ofi point. Thus, when usedv as a power output tube, the Waste is very much reduced. Y

Although a tube having three auxiliary electrodes has been taken as an example, it is obvious that the invention is also directly applicable to tubes having four and more auxiliary electrodes. Particularly since in many hexodes, heptodes and octodes the first auxiliary electrode is rod-shaped, tubes of this kind may be used quite satisfactorily in the circuit arrangement described. Moreover, for obtaining the desired effect it is not essential that the first auxiliary electrode should be rodshaped.

While I have indicated the preferred embodiment of my invention of Which-I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact form illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device having an envelope containinga cathode surrounded by a control grid, screen grid and anode, and a pair of rod electrodes parallel to said cathode and positioned between the cathode and control electrode, said rods being directly electrically connected to each other and to the screen grid electrode.

. An.electron discharge device having an envelope containing a cathode, control grid, screen grid and. anode, and a space charge electrode grid and cathode, an input circuit connected to said control grid and an output circuit connected to said anode and a source of voltage having its positive potential connected to said anode through said output circuit, a direct electrical connection between said screen grid and said space charge electrode, and a resistor connected between the positive side of said voltage source and the connection to said screen grid and space charge electrode.

3. An electron discharge device having an envelope containing a cathode, control grid, screen grid and anode, and a space charge electrode comprising a .pair of rods on opposite sides of said cathode and between the control grid and cathode, the spacing between said rods and cathode being greater than the spacing between the nearest portion of said control grid and said cathode, an input. circuit connected to said control grid and an output circuit connected to said anode and a source of voltage having its positive potential connected to said anode through said output circuit, a direct electrical connection between said screen grid and said space charge electrode, and a resistor connected between the positive side of said voltage source and the direct electrical connection to said screen grid and space charge electrode. l

4. An electron discharge device having an envelope containing a cathode, control grid, screen grid and anode, and a space charge electrode comprising a pair of rods on opposite sides of said cathode and between the control grid and cathode, the spacing between said rods and cathode being greater than the spacing between the nearest portion of said control grid and said cathode, an input circuit connected to said control grid and an output circuit connected to said anode and a source of voltage having its positive potential connected to said anode through said output circuit, a direct electrical connection between said screen grid and said space charge electrode, and a variable resistor connected between the positive side of said voltage source and the direct electrical connection to said screen grid and space charge electrode.

, JOHAN LODEWIJK HENDRIK JONKER. 

